1. Field of the Invention
The present invention relates to a profile producing method and a profile producing apparatus for producing a profile representative of the association between the colors on a color image and the color data in accordance with which the color image is outputted, in an output device such as a color printer and a printing machine for outputting color images in accordance with image data including color data.
2. Description of the Related Art
Hitherto, it is widely performed that a color image is outputted by an output device such as a color printer and a printing machine in accordance with, for example, image data obtained through reading an original image by a color scanner and the like, and image data generated by a computer. At that time, when it is intended, for example, to output a color image which is very close in color to an original image before reading by a scanner, or to output a color image having a desired color representation, it is an important problem as to what color is reproduced on the color image in accordance with color data included in image data fed to the output device for outputting the color image. The association between the color data and the color on the color image outputted is referred to as a profile of the output device.
FIG. 19 is a flowchart useful for understanding the conventional method of producing a profile. Here, there will be explained, by way of example of the output device, a printing machine four printing a color image in accordance with image data including color data representative of dot % for four colors of cyan (C), magenta (M), yellow (Y) and black (K).
To produce the profile of the printing machine, for example, a computer is used to produce image data representative of a color chart consisting of a plurality of color patches associated with a plurality of sorts of color data obtained through sequentially varying dot % on each of four colors of C, M, Y, K (step e1 of FIG. 19), the image data thus produced are transmitted to the printing machine to print the color chart (step e2), and the printing machine produces a print sample of the color chart (step e3). Next, a plurality of color patches on the print sample of the color chart are subjected to a colorimetry by a calorimeter (step e4) to obtain the association (here, it is referred to as the “association M”) between the color data transferred to the printing machine for output of the color chart and chromaticity values of XYZ values of XYZ color system determined by, for example, CIE, which chromaticity values are obtained through measurement of the color chart (step e5).
The association M between the color data and the chromaticity values is restricted in number of color patches constituting the color chart, and thus it is an association corresponding to the coordinate points rather rough and scattered on a color space. Therefore, such an association M is too rough to express the profile of the printing machine.
In view of the foregoing, in the next step e6, a table T representing the profile of the printing machine is produced in accordance with a computation (it is referred to as a “computation A”) for producing a table including an interpolation arithmetic operation-processing and the like.
As the computation A, it is possible to preferably adopt a computation scheme, for example, as proposed in Japanese Patent Application Laid Open Gazette Hei. 10-126633, that the association between the color data and the chromaticity values, which corresponds to each of sides on a three-dimensional shape (corresponding to a cub in case of a three-dimension) defining an external form of an area (a color reproducing area) to be expressed by the printing machine, on CMYK color space, is determined, then the association between the color data and the chromaticity values, which corresponds to coordinate points on each surface encircled by a plurality of sides, is determined, and finally, the association between the color data and the chromaticity values, which corresponds to coordinate points inside the three-dimensional shape.
The use of the table (the profile) thus produced makes it possible to print a color image of a desired color representation using a printing machine.
To determine a profile of an output device through adoption of the above-mentioned method, there is a need to measure a color chart composed of a large number of color patches outputted from the output device. This is associated with such a problem that it takes a great deal of time. An adoption of the computation scheme, which is proposed in Japanese Patent Application Laid Open Gazette Hei. 10-126633, makes it possible to considerably reduce the number of color patches as compared with the earlier technology. However, even in the event that such a computation scheme is adopted, there is a need to output and measure hundreds of color patches in order to produce a table (a profile) excellent in precision.
As a method in which the above-mentioned problem is improved to allow the use of a small number of patches, Japanese Patent Application Laid Open Gazette Hei. 10-136219 proposes a technology that a table produced beforehand on a reference output condition is corrected in accordance with data obtained through colorimetry of a small number of color patches outputted on the correction output condition, so that a new table is produced.
However, according to the proposed technology in Japanese Patent Application Laid Open Gazette Hei. 10-136219, while it is possible to admire such an idea that an existing table produced beforehand is utilized. However, a precision of a table newly produced considerably depends on the existing table utilized for producing the new table. Further, according to the proposed technology in Japanese Patent Application Laid Open Gazette Hei. 10-136219, it is impossible to represent non-linear characteristics between the color data and the chromaticity values. Thus, also in this respect, it is a problem in the point of precision.